Studies on Particle-Wall Interactions in Particle-based High Temperature Concentrating Solar Thermal Systems

Abstract

Next-generation (Gen3) concentrating solar power (CSP) systems use solid particles as the heat capture, transfer, and storage medium to reach operating temperatures above 700 °C, but the continuous contact between flowing particles and component surfaces drives severe material degradation through the coupled action of high-temperature oxidation and abrasion. This thesis examines particle–wall interactions in particle-based high-temperature CSP through two complementary studies. First, the combined oxidation–abrasion performance of four candidate alloys, stainless steel 316 (SS316), Incoloy 800H, Haynes 230, and Inconel 718 (In718), is evaluated in a moving bed of dense sintered bauxite particles (CARBO HSP 40/70) at room temperature, 700 °C, and 800 °C. The iron-based alloys exhibit relatively stable abrasion behavior across the temperature range, whereas the Ni-based alloys undergo intermittent severe degradation at 700 °C but improved long-term wear resistance at 800 °C, where enhanced oxide regeneration and mechanically mixed layer development provide increased surface protection. Second, a nanoscale multilayered Cr/Cr2N coating deposited on In718 by reactive unbalanced DC magnetron sputtering is tested against uncoated In718 for 324 h at 700 °C and 800 °C under combined oxidation and abrasion. The coated specimens show no measurable substrate mass loss at either temperature, while uncoated In718 at 700 °C spalls at an average rate of 4.47 mg/h, identifying nanoscale Cr/Cr2N multilayers as a viable route to extending component service life. Collectively, these studies indicate that a self-replenishing mechanically mixed layer forms naturally under sustained particle contact and provides an additional protective barrier against abrasion, provided the underlying substrate or coating is capable of maintaining oxide-scale adhesion and mechanical stability under dynamic particle contact. Because the alloy is then not directly exposed to the abrasive medium, this behavior theoretically allows lower-cost materials to be used in particle-handling components, and provides a basis for the design of longer-lived, more economical receivers for Gen3 CSP.